The long term goal of this research is to understand the mechanisms by which synapses in the brain are changed by activity and environmental stimuli. We focus on a specific type of synaptic receptor - the NMDA class of glutamate receptor - that plays an important role in long-term changes in synaptic function, the regulation of cell-death, and the generation of patterned activity in neuronal networks. These processes require that the NMDA receptors allow the appropriate amount of calcium ion to pass through its pore and enter the neuron, and be blocked by extracellular magnesium ion over an appropriate range of membrane potentials and concentrations. Thus, in order to understand the molecular bases of synaptic plasticity, we must understand the mechanisms that determine the divalent cation permeability and block of NMDA receptors. We will use recombinant DNA technology to make point mutations in the receptor protein, and then study the altered functions of mutant receptors (expressed in oocytes) using single-channel patch clamp methods. We will investigate how the pore residues, and the subunit composition of the receptor, determine the affinity for calcium and magnesium, if the channel conductance is regulated by electrostatic mechanisms, and the mechanisms by which subconductance levels are generated. We will also investigate the subunit composition (type and copy number) of receptors by studying the patterns of subconductance states that are apparent in receptors composed of different mixtures of wild type and mutant subunits. An understanding of the molecular mechanisms of operation of NMDA receptors channels will provide insight into the basis of developmental, degenerative and other diseases of the nervous system.